With the explosive growth of automotive electronics, will more and more luxury cars endanger passenger safety? This is the origin of the problem of car over-electification. What measures should the design engineer take to avoid potential dangers?
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Recalling the past (not so far away), driving your dad's classic car, AM/FM radio, tape recorders and car air conditioners mark the highest level of luxury cars of that era. Today, many people can't imagine that the family's road trips are almost equipped with satellite navigation GPS, separate DVD players for each passenger, in-car climate control, heated seats, cruise control, wireless access, and reminder drivers. The voice prompt function of the light is always on, and the engine should continue to supply power to these electronic systems. Otherwise, these devices will become flashy furnishings.
With the increase in automotive electronics and electrical accessories, how can manufacturers meet their requirements by providing enough power? What happens if there is a voltage surge or fall? Will more luxurious cars endanger the safety of passengers? What solution is needed to ensure that a highly electrified car maintains sufficient power?
Accessories power consumption is on the rise
Automotive electronics and electrical equipment are increasing at an average rate of more than 110W per vehicle per year. Recently, systems driven by mechanical and hydraulic pressures have been driven by electricity, and most of the demand for electrical energy comes from this. The anti-lock braking system (ABS) that emerged in the 1980s has an electronic control unit with a storage capacity of approximately 8 KB; modern fifth-generation ABS hardware is equipped with 128 KB of memory, which is only 40% of the size of the earlier system. Due to the ingenuity and innovation of design, modern electrical/electronic systems typically require less power than originally introduced.
The following table summarizes the main subsystems (and loads) of modern automotive automotive electrical/electronic systems:
Engine management
Multimedia and heating, ventilation and air conditioning (HVAC)
Body electronics
Chassis electronics
Lighting (external and internal)
Future system
The electrical loads listed in the table are a mixture of continuous and intermittently operating components. However, the components of an automotive power charging system must include at least an alternator, battery, and power distribution system (ie, PowerNet), which must fully and continuously support engine management functions as well as most multimedia and HVAC functions, and based on driving conditions. And consumer use supports the rest of the category of automotive electronic systems.
The two categories (engine management, multimedia, and HVAC) automotive electronics systems in the table require an automotive power system to provide 102A of current. This is important. To describe the current state of the accessory overload, it is important to note that in order to support the 102A load without increasing the battery, the alternator must have approximately twice the rated current - 204A. The reason is that the car alternator can only generate half of the energy when the engine is running at low speed and idling. This requires a large alternator, which must provide 2,840W of power on a PowerNet with a nominal system voltage of 14.2V.
If the power consumption of the remaining four subsystems is included in the load survey of the vehicle with different duty cycles, it is possible to easily exceed the power supply capacity of the alternator. When this happens in a current car, the PowerNet voltage drops until the system voltage matches the 12.8V voltage inside the battery, at which point the battery begins to provide a portion of the total power load. This effect is known as battery contribution.
Battery distribution is a periodic event that randomly supplies power to uninterrupted electrical loads, such as automatic temperature control in the passenger compartment, rotating steering wheel events, or powering a deterministic load selected by the consumer, such as an audio system. Or navigation assistant. These periodic events are the cause of battery drain and eventually result in the need to replace the battery.
The last point to note about this watch is that if you consider the intermittent load of subsystems such as body electronics, lighting, and chassis electronics, the demand for car charging systems is really accessory overload. Future systems will continue this trend.
Automakers are therefore taking steps to reduce the overload of electrical systems caused by the proliferation of electronic systems. These include: improving the efficiency of existing electrical accessories; functional integration to eliminate redundant control electronics, thereby reducing the power consumption of the control system; reducing mechanical transmissions, for example, enabling ABS innovations to be smaller and lower The power consumption provides the expected functionality. (rewrite)
Power demand is endless
The reality remains: in the near future, attachment overloads will continue to be as strong as consumers need more and more new features and functions. The evolution of the 4th generation automotive electronics system can be seen from the figure below.
From 1968 to the 1970s, the first generation of automotive electronic systems, including electric power windows, electric door locks, air conditioners, electronic fuel injection, and electronic ignition, were necessary and evolved to meet the emission regulations of that era. To use electric power steering.
From the 1980s to the early 1990s, the second generation of automotive electronic systems included ABS, anti-theft systems and more advanced electronic engine control systems to meet the requirements of regulations that limit emissions. The second generation of automotive electronics systems is made possible by the use of software control functions and dedicated electronic control units, such as the early engine control unit (ECU) that manages fuel through sensor-based closed-loop control and electromechanical transmissions that replace older mechanical systems. Spark plug discharge and recirculation of exhaust gases.
The third generation of automotive electronics is made possible by the introduction of more powerful microprocessors, such as the 8080, which replaces the 8080 and handles more control functions. This has led to more advanced features such as multiplexed communication and distributed computing functions, cruise control, navigation and more automated air conditioning systems, improved gearboxes, automated human-powered transmissions, and adopted More advanced airbags. In the third generation of automotive electronics, in-vehicle entertainment systems use digital signal processors (DSPs) to improve the performance of distributed electronic system architectures and extend applications for multiplex communications such as controller area networks (CANs).
With higher levels of distributed automotive electronics, it is possible to free up new space from the dashboard panel because only control information needs to be read. An example of this trend is the sound system of the 1990s, in which the radio movement and the audio amplifier stage are mounted in the rear window sill area of ​​the car body, leaving only the display and switches on the dashboard panel. Similar trends have emerged in systems such as in-vehicle climate electronic controls, navigation systems, CD changers, and the like.
In the fourth generation of automotive electronics systems, microprocessors and digital signal processors are becoming more popular in automobiles. In these 21st century systems, each car's automotive electronics system uses 40 to 80 microprocessors and 35 to 100 motors. The new system is controlled by software and relies extensively on the availability of inexpensive and robust memory hardware.
In the future, the number of electronic systems in a car may not grow as fast as the second generation, but the software system will grow exponentially. For example, one trend that is currently being presented is to upgrade online diagnostics (OBD) to the next generation of OBD1 through immune system engineering. This trend is due to the fact that the current system complexity is so high that nearly 2/3 of the failure modes are simply uninterpretable and will continue to deteriorate.
To diagnose future automotive electronic systems, online computing software will need to be expanded to perform diagnostics, as future systems will include more than an order of magnitude more electrified high-security subsystems than existing systems. These high-security subsystems are included here. The electrified subsystems and more subsystems discussed. Currently, electronic throttle control (ETC) and electronic power steering (EPS) have been extended to electronic stability program (ESP) systems to manage automotive longitudinal motion control to electronically controlled brake (ECB) systems. These subsystems become the sixth category listed in the table.
PowerNet stability
With the increase of automotive electronic systems and the burden of automotive power supply systems, how can design engineers mitigate the effects of various automotive electrical equipment? Although the average power demand of these powered devices continues to grow at a rate of 110W per year, this is actually not a decimal, as we have seen that the power consumption of automotive electronic systems has overloaded the power supply system. The question is what is the “last straw†that crashes the car's power supply system? When will this happen?
When the behavior of a chaotic system is affected by some kind of stress factor, if the growth of the stress factor is silent, it will eventually approach a point of collapse or tipping point. This is happening on cars as the demand for automotive PowerNet increases. From the point of view of grid stability, this situation is not so serious because of the stabilizing effect of the car battery.
Problems caused by PowerNet's instantaneous fluctuations
As mentioned above, 21st century automotive electronic systems are highly software dependent and, therefore, increasingly susceptible to PowerNet variability, and crowded and messy power distribution networks are more sensitive to transient changes in power usage. Manufacturers need to install power line filtering and larger capacitor banks in more sensitive electronic modules to address the problems faced by deteriorating power distribution networks. In fact, all electronic modules still have different levels of noise immunity; sometimes a combination of a degraded power distribution network and the module's own load switch can cause software failure. The reason for this confusion is that the microprocessor or some supporting logic functions are susceptible to simultaneous power line fluctuations, surges, and load drive pulses.
Currently, automakers are looking to use supercapacitor distributed modules or local electrical energy storage devices to provide smooth and stable PowerNet to ECU-related locations. The following diagram depicts a hierarchical view of the balance between distributed electronic modules, electromechanical actuators, and supercapacitor partially energy storage devices.
In this highly simplified description, the supercapacitor distribution module or double layer capacitor (DLC) is placed close to high energy consumption loads such as EPS (1.2 kW), electromechanical brakes (1 to 2 kW) and new lighting systems (like recently White LED headlights appear). The local distributed module supplies power to the peak load, avoiding strong fluctuations in the 14V power line from the alternator and battery.
The switching of high-energy loads, as highlighted in the above figure, has significant interference with the automotive power distribution network, 14V PowerNet. For example, in some of the newly proposed EPS designs, the electric power steering (EPS) system has a power demand of 130A, up to 160A. In the past, it was assumed that EPS power demand was in the range of 85A (1.2KW) to 130A (1.8KW). If it exceeds that range, it means that PowerNet is in the worst power supply state, which may endanger the normal operation of EPS. When the engine is almost idle and the continuous load is already 27A plus 67A or 1.3KW, adding 1.2 to 1.8KW of instantaneous load to PowerNet means that the voltage distribution of the power distribution system is 14.2V to 12.8V; this is also the battery potential. The range of fluctuations. If the voltage of the power distribution system drops by 10%, then the darkening of the headlights will be obvious, and the EPS performance will be degraded, not to mention the problems caused by PowerNet transient fluctuations being transmitted to all other connected ECUs.
Load smoothing method
The first half of this article depicts the transient overload of automotive accessories, which will be further explained by simulation. In the illustrated process, engine management and some climate control electronics systems are also working continuously, assuming that the electric assist system (EPS) is working. Assume that the EPS draws 90A from the car's power line (PowerNet) for 300ms, for example, making a lane change on a hard road or parking at a low speed in the parking lot.
In the first case shown below, the EPS is activated when PowerNet is relatively heavily loaded, but the supercapacitor power distribution module is not installed. Connected loads represent 27A engine management, 55A climate control and 15A remote electronic control unit (ECU). For example, the remote ECU may be an audio module and is intentionally shown to be filtered and smoothed using a local electrolytic capacitor.
Figure: This PowerNet powers the EPS operating, but no supercapacitor distribution module is installed.
In the above figure, the car charging system is represented by an alternator and a lead-acid battery. In this case, the battery was modeled in more detail using the Simplorer electrochemical modeling tool from Ansoft's automotive toolbox. PowerNet is highly simplified to four sub-circuits modeled by wire gauge resistors, including engine control, cabin climate control, local ECU and EPS (far right). PowerNet distribution points are labeled as PDBs or power distribution boxes.
When the EPS is working, the following figure depicts the PowerNet transient fluctuations caused by the above circuit. Note: When the power distribution network is stable, the alternator provides the initial charging current to the battery.
Figure: PowerNet transient fluctuations when EPS is activated
In the curve above, from left to right, from top to bottom are: alternator output current, battery current, battery voltage, EPS current and local ECU terminal voltage. Note that the battery requires 20A of continuous charging current before the EPS is momentarily activated. In this simulation, it is assumed that the battery state of charge is low and charging is required. The key point is the high variability of the ECU terminal voltage: 13.8V to 13.2V, then to 12.2V, and then back to 13.2V. This is a very destructive transient voltage fluctuation that exceeds the smoothing capability of large electrolytic filter capacitors.
Many such transient fluctuations occur in the automotive power distribution network, so that the automotive power environment is full of such noise, allowing various ECUs to be affected by a wide range of up and down fluctuations on the power line.
Figure: This PowerNet circuit powers the activated EPS and contains a supercapacitor distributed module (top right)
The above picture is identical to the previous PowerNet circuit diagram, but with the addition of a super distributed module placed at the EPS load point. This super module is a standard automotive design product that provides a stable and smooth PowerNet like a battery near a large electrical load. As in all other places, where super-distributed modules exist, smoothing can be easily observed on PowerNet and ECU voltages.
Figure: Supercapacitor distributed module smoothes power supply fluctuations on PowerNet when EPS is activated
As can be seen in the above figure, PowerNet with a supercapacitor distributed module shows much better response behavior. Note: The displayed scale has changed and the range of power supply is much smaller than when the supercapacitor module is not used. The important point is that the EPS current does not change, so its function remains the same. The outstanding feature of the supercapacitor distributed module is that power line interference (lower right trace) on the terminal voltage of another branch circuit of PowerNet that supplies power to the local ECU is greatly reduced.
The benefits of distributed modules or local energy storage based on carbon supercapacitor technology are: Stabilizing PowerNet is highly efficient, helping to smooth and stabilize the power line even in the remote branch circuit of the car.
In the near future, automotive electronics functions and features will continue to grow, with the accompanying increase in accessories that overload the power distribution system. Large continuous power loading is pushing the car charging system to overload, and the load transient voltage fluctuations generated by more and more and more power-consuming devices make it very likely that a very complex and highly distributed computing network will be damaged.
In order to see this clearly, look at the cooling capacity of an air-conditioner compressor on a typical car and an air conditioner installed in a medium-sized American home. It can be seen that the air-supply motor in the car is actually much larger than the power consumption of the home central heating system. many. Many other in-car electrical equipment are similar. All of these electrical devices are installed in very limited spaces and often "hug" heat and vibration.
The supercapacitor distributed module can replace two or three lead-acid batteries to provide a power solution for passenger cars, and it provides sufficient filtering for the power system. To some extent, it can be called the imminent tipping point. For automakers, supercapacitor distributed modules will be essential to reschedule PowerNet and triple the voltage of the power distribution system to the proposed 42V standard. By relying solely on its function, the current in the power distribution system discussed herein can be reduced by a third.
In addition, in order to meet the requirements of specific functions, some transitional systems have been developed in this direction, using the supercapacitor distributed module technology to raise the local 12V battery supply voltage to 30V or higher; EPS is such a function, micro hybrid ( Related to the idle parking system) is another example of providing higher voltages in automobiles.
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